DisplacementDisplacementChange in position of an object
Frame of reference◦A point against which position is measured
Example: A train traveling between stations◦It is in motion when measured against the
track.◦It is stationary when measured against a seat.
Displacement (Displacement (xx))Straight line distance from the initial
position to the final position (change in position)
Can be positive or negative
Displacement (Displacement (xx))What is the
displacement for the objects shown?
Answer: 70 cm
• Answer: -60 cm
Displacement Sign ConventionsDisplacement Sign Conventions
Uses a coordinate system•Right (or east) ---> +◦Left (or west) ---> – ◦Up (or north) ----> +◦Down (or south) ---> –
SpeedSpeed
Speed does not include direction while velocity does.
Speed uses distance rather than displacement.
In a round trip, the average velocity is zero but the average speed is not zero.
Average VelocityAverage VelocityDisplacement in a given time
Average Velocity = (ΔX/Δt) = displacement/time interval
Average VelocityAverage VelocityDescribe the motion of
each object.Answers
◦ Object 1: constant velocity to the right or upward
◦ Object 2: constant velocity of zero (at rest)
◦ Object 3: constant velocity to the left or downward
Instantaneous VelocityInstantaneous VelocityVelocity at a single instant of time
Speedometers in cars measure instantaneous speed.
Determined by finding the slope at a single point (the slope of the tangent)
Book Problems
Heather and Matt take a 34 minute walk eastward along a straight road to a store 2.0 km away. What is their average velocity in m/s?
0.98 m/s to the east
Book Problems
Eugene is 75 km due south of Salem. If Joe rides from Salem to Eugene on his bike in 6.00 hr, what is his average velocity?
3.47 m/s to the south
Book Problems
A bus traveled south along a straight path for 3.2 h with an average velocity of 88 km/h, stopped for 20.0 minutes, then traveled south for 2.8 h with an average velocity of 75 km/h. What is the average velocity for the total trip?
20.83 m/s to the south